Vacuum tube



8- 1934. Y. B. J. GROENEVl ILD ET AL 1,

VACUUM TUBE Filed March 15, 1930 INVENTORS Y. B. F. J. GROENEVELD E. 005 R \s ATTORNEY Patented Aug. 28, 1934 PATENT OFFICE VACUUM TUBE Yme Bouwinus Folkert J an Groeneveld and Ekko Oosterhuis, Eindhovcn, Netherlands, assignors to Radio Corporation of America, a corporation ojf Delaware Application March 15, 1930, Serial No. 436,010 7 In the Netherlands May 18, 1929 2 Claims. (Cl. 250-27.5)

This invention has'reference to an arrangement :comprising an electric discharge tube the incandescent cathode of which can be'heated directly or indirectly by means of alternating current; It also relates to an electric discharge tube and to a socket for use in suchan arrangement.

It is commonly known that when'the incandescent cathode of a discharge tube is heated by means of alternatingcurrent, the anode current 210 mayvary, which whenthe tube isconnected to a telephone or loudspeaker may become =manifested by a humming tone. The invention has for its object to obviate this unfavorable result of heating the incandescent cathode by alternating current, or else to decrease it to aconsiderable extent.

It" has been foundthat the humming tones'are partially induced by leak-currents flowing between the -current leads of thegrid and the incaridescent cathodefior its heating element and passing across the grid leak by which the grid is-connected to the cathode. These alternating currents bring about between the endsof the grid resistance,and consequently betweenthe grid and 5 the incandescent cathode, potential variations that cause the anodecurrent to vary, which may bring about the'hummingtones above referred'to.

According to the invention, these fluctuating leak currents which pass throughthe grid leak are obviatedby the arrangement of a conductive memberbetween thegrid current lead and the current leads of the cathode or its heating elemerit and by member to the conductor which connectsqthe cathode to the grid leak. The'c'onductive member may extend throughout the whole length of the conductors between which it is arranged orfor part of that length and may consist of various parts. Preferably, the conductive member, which 40 may be cylindrical, iscaus'ed to surround the grid current lead.

In an electric discharge tube for use in the ar rangement described, the grid current lead and the current leads of the cathode or its heating element are separated, at least for part of their length, by a conductive member which may consist of several parts. Preferably, this conductive member *i's'so shapedas to surround the grid current lead,iit being, for example, cylindrical. In some cases it is possible to electrically connect the conductive member in the tube or the base to a currentlead of the cathode or its heatingelement. I v r A socket according to the invention for use in the arrangement described'contains'a conductive electrically. connecting the'said member which is arranged at least forpart of the length between one of the current supply members of the socket and the remaining current sup ply members and which consists of one or more Parts. Again, this member may be-so shaped as to surround'one of the current supplying members, theconductive member being in some cases electrically connected within the, socket to one of the current supply members.

In order that the invention may be clearly understood and readily carried into effect, one embodiment of the invention will be described more fully with reference to the accompanying drawing.

-Figures '1 and. 2 illustrate diagrammatically L10 electric discharge tubes'havingadirectly or inchrectly heated cathode and part .of the circuit arrangements in which thesaid tubes are included. Figure 3 shows, by way of example, an electric discharge tube according to the invention, and

Figures land 5 are a planand a-sectional view respectivelyof one construction of a socket according to the invention.

The invention will be more clearly understood by reference to'Figures 1 and 2. Referring to Figure 1, l designates an electric discharge tube comprising a directly heated cathode 2, a control grid 3, and an anode 4. The cathode can be 'heatedby means of a current generated in the transformer winding 5. The grid is connected through a lead 6, a grid leak 7, and a source'of grid voltage 8 to the middle point of the transformer winding'fi. The insulation-between the current leads of the grid and the filament will have an electric resistance which is designated in the figure by a dotted line 9. The transformer winding 5 will pass an alternating current through the circuit which is constituted 'by thesaid resistance 9, the lead 6, the grid leak '7, the source of voltage 8, and the lead that connects the source of voltage to the middle point of the transformer winding. This alternatingcurrent will bring about between the ends of the :grid leak 7 variations in voltage which vary the potential between the control grid 3 and the incandescent cathode 2 so that also variations in the anode current will be brought about. By tapping the resistance 9, say at 10,

and connecting this point directly to the middle point of the transformer winding 5 by a connection indicated in the figure by -a dotted line 11, the current produced in the resistance 9 by the transformer voltage will no longer pass through the "grid leak 7 but through the electrical connection 11 so that by this current no potential 110 variations are brought about between the ends of the grid leak.

The discharge tube 12 shown in Figure 2 comprises an anode 13, a control grid 14, and an indirectly heated cathode 15 the heating element of which is designated by 16. This heating element is supplied from a transformer winding 17. The grid of the discharge tube shown in this figure is likewise connected by a grid leak 18 and a source of grid voltage 19 to the middle point of the transformer winding 17 to which the indirectly heated cathode 15 is also electrically connected. The resistance between the grid 14 and one of the pole wires of the heating element is designated in this figure by 20. It is, of course, obvious that with this method of connection, an alternating current brought about by the winding 17 will likewise pass through the grid leak 18 and produce therein potential variations. With this method of connection, these potential variations can likewise be obviated by tapping the resistance 20, say at 21, by means of the conductive wire 21 and by connecting the latter to the middle point of the transformer winding.

The resistances designated in Figures 1 and 2 by .9 and not only comprise the resistance existing on the surface of the insulating wall of the discharge tube between the lead wires of the grid and the cathode or its heating element, but also comprise the resistance between the current leads of the grid and the cathode or its heating element whether these current leads are internal or external to the discharge tube.

The invention consists therefore in that the electric resistance existing between the current leads of a grid and the cathode or its heating element is tapped and the tapping point is connected to the point of connection of the grid circuit to the incandescent cathode. This can be ensured by arranging a conductive member between the current lead of the grid and the current leads of the cathode or its heating element and by connecting the said member to the conductor that connects the cathode to the grid lead. It is, of course, obvious that this conductive member does not always necessarily extend throughout the whole length of the current leads. At those points where the insulation between the current lead of the grid and the current leads of the cathode or its heating element practically is perfect the conductive member can be dispensed with without materially lowering the results obtained in accordance with the invention.

The discharge tube shown in Figure 3 comprises an indirectly heated cathode consisting of a tube of small diameter 23 which is externally coated with a highly electron emitting substance and which contains a heating element 24. This element is constituted by a U-shaped wire and is insulated from the operative portion of the cathode 23 by insulating material 25. The discharge current is supplied to the cathode through a supporting wire 26 and the heating current of the heating element may be supplied through supporting wires 2'7 and 28. The cathode is surrounded by a grid 29 consisting of a helically wound wire and carried upon a supporting wire 30. The grid is surrounded by a cylindrical anode 31 secured to a supporting wire 32. The various supporting wires are secured to and taken through the pinch or press 33. The grid supporting wire is partially surrounded by a small insulating tube 34 which may be of glass -insulating tube 34 which is sealed to the press facilitates mounting the conductive ring 35 but it is also possible for this ring which, for example, may be by a short tube of small diameter to be mounted directly on the press. Alternatively, the conductive member may be constituted by an annular streak of conductive material applied upon the press.

The supporting wire 30 of the grid is connected to the lead 37 which connects to a contact pin 38 secured to the insulating base 39. This base has also secured to it a contact pin 40 to which the cathode supporting wire 26 is connected. The contact pin 38 is partially surrounded by a cylinder 41 of conductive material enclosed Within the base 39. Preferably the cylinder 41 slightly extends beyond the insulating material of the base and is connected by the conductive wire 42 to the contact pin 40.

Generally the major part of the leak currents flows between the grid current lead and the leads of the remaining electrodes along the surface of the press. Consequently, satisfactory results can be obtained by providing the ring 35 shown in Figure 3. However, a slight current passage between the current leads may occur at other points, for example through the insulating material by which the said current leads are separated. According to the invention, the influence of these currents can likewise be obviated by arranging at the said points, for example in the insulating material, a conductive member which is directly connected to the point of connection of the grid circuit to the cathode. A member of the kind referred to enclosed within insulating material is, for example, the ring 41 shown in Figure 3. A conductive member which surrounds the grid current lead wholly or in part may likewise be arranged, if necessary, in the press.

It is, of course, obvious that it is not possible in many cases to connect the conductive memher to the current lead of the cathode within the discharge tube or within the base. Thus for example, as may be seen from Figure 1, it will be frequently necessary for the conductive member to be connected outside the discharge tube to the middle point of the transformer winding that supplies the heating current of the cathode. In this case it will be necessary for the part of the conductive member that is enclosed within the discharge tube to be provided with a separate leading-in wire which permits establishment of the above-mentioned connection outside the discharge tube.

The socket shown in Figures 4 and 5 comprises a plate 43 of insulating material having a depending flange at the edge. This plate has secured to it by screws 48 four contact sleeves 44, 45, 46, and 47. The plate has mounted on it in addition four terminals 49 connected by small conductive strips 50 to the contact sleeves. One of the current supply members of the valve-hold er which is intended to receive the contact pin of the grid of an electric discharge tube is partially surrounded by a small conductive plate 51 enclosed within the plate 43. This plate 51 can press and enclosing cathode, grid, and plate electrodes, a current supply lead for each of said electrodes sealed into said press, said leads projecting side by side from the elongated end sur face of said press, a metal member embedded in and projecting above the end surface of said press on oppositesides of said grid lead between said grid lead and the adjacent'cathode and plate leads, and a conductive connection between said metal member and said cathode.

2. An electron discharge tube comprising a sealed envelope having a stem with a flattened press and enclosing cathode, grid, and plate electrodes, a current supply lead for each of said electrodes sealed into said press, said leads projecting side by side from the elongated end surface of said press, a metal guard ring surrounding said grid lead with one end embedded in said press and the other end projecting above the end surface of said press concentric with said grid lead and interposed between said cathode lead and said plate lead, and a conductive connection between said guard ring and said cathode.

YME BOUWINUS FOLKERT JAN GROENEVELD.

- EKKO OO STERHUIS. 

